This invention relates to a semiconductor laser device capable of easily controlling the polarization characteristics of the output light.
Optical communiation and measurement using semiconductor lasers have come to find acceptance for practical use. The semiconductor lasers have characteristic features such as small size and light weight, low working voltage, high operational efficiency, and direct quick modulation as compared with other lasers. Now that improvements in service life, reliability and output are making steady progress, there is a high probability that the price of semiconductor lasers will fall as mass production and range of applications are expanded.
Recently, a polarization-preserving optical fiber has been developed and optical communication making use of a multiplicity of planes of polarization has been proposed. Further as studies are progressing on an optical fiber interferometer using a semiconductor laser as a light source and on use of long optical fibers as sensors such as for temperature, pressure, and magnetic field, the polarization-plane characteristics of the output light of semiconductor lasers have come to attract the attention of researchers.
With the ordinary gas laser, it is customary to obtain a straight polarized output by regulating the plane of polarization of the output light by means of a discharge tube incorporating therein Brewster windows. In this case, the polarization ratio defined as the ratio of the intensity of the main component of polarized radiation to the intensity of the component of polarized radiation perpendicularly intersecting the main component is obtained on the order of 1000 to 1. In contrast, with the semiconductor laser, the cleaved facet of the semiconductor crystal is used as the reflecting face for the resonator and the polarization characteristic based on the anisotropy of reflectance on the cleaved facet are utilized. Because the ability of the cleaved facet to control the polarization is smaller than that of the Brewster window, the polarization ratio of the output light from the semiconductor laser normally falls on the order of 20 through 30 to 1, and 100 to 1 at most.